The invention is based on an adjusting device for a sun roof of a motor vehicle. An adjusting device is already known (German DE-OS 42 29 439), which has an electric motor for driving a sun roof whose position has to be regulated precisely. The position of the sun roof is detected by an incremental position encoder and a single absolute position encoder. The absolute position encoder is embodied as a microswitch, which can be actuated via a cam wheel. This cam wheel distinguishes among four ranges (positions) of the sun roof, but only two switching edges can be evaluated by approaching them directly. In a sun roof, essentially three positions of the roof are possible: a null position with the roof closed, a terminal position in the raised mode, and a terminal position in the sliding mode. Accurately ascertaining the position of the sun roof is done by evaluating the electrical signals of the one absolute position encoder and by evaluating the electrical signals of an incremental position encoder. Under certain conditions, such as if the power fails or the sun roof is adjusted by hand, the position derived from the encoders no longer agrees with the actual position of the sun roof. Hence it is no longer possible to detect the range of position the sun roof is in unequivocally, and this can cause the sun roof drive system to react incorrectly or even fail. The known adjusting device, with only one absolute position encoder, is therefore not statically stable, because of the multiple interpretations that can be made of the switching signal output by the absolute position encoder. Moreover, in the known device it is indispensable that the adjusting motion of the sun roof be stored in a microcontroller that is provided. Yet a possible power failure means that the system no longer has any information on the current position of the sun roof, and may possibly identify the wrong range, thus leading to incorrect reactions on the part of the system or to an undesired change in position of the sun roof.